Scientists have created a real-life Speedy Gonzales by genetically engineering a mouse which can easily outrun its natural cousins.

When let loose on a treadmill in the laboratory, the mouse ran for up to six hours without stopping, covering as many kilometres before finally taking a rest. Normal mice gave up after covering just 200 metres at the same speed.

The souped-up rodent consumes 60% more food than other mice, but remains fitter and leaner. Surprisingly, the species also lives longer and is able to breed until a later age.

Richard Hanson and Parvin Hakimi at Case Western Reserve University in Cleveland, Ohio, created the mouse by altering a gene that controls a key enzyme called PEPCK-C which is involved in energy metabolism.

The genetic tweak directs energy production overwhelmingly to the animal's skeletal muscles.

The researchers have now bred nearly 500 supermice which are instantly recognisable by the amount of time they spend running around their cages.

"They are metabolically similar to Lance Armstrong biking up the Pyrenees," said Richard Hanson, professor of biochemistry and lead author of the study, published in the Journal of Biological Chemistry.

Normally, female mice are unable to reproduce beyond the age of one, but some genetically modified females were still reproducing at 2.5 years old.

The mice were created as part of a five-year ongoing study into the role of the PEPCK-C enzyme in muscles and fatty tissues. Unlike natural mice - and humans - the supermice mainly burn fatty acids for energy. They produce only tiny amounts of lactic acid, the byproduct that builds up in muscles and causes cramps when they are forced to work with insufficient oxygen.

In one exercise, the mice were set running on a treadmill at a 25-degree incline. The speed was turned up by two metres per minute every minute until the mice gave up through exhaustion. While normal mice stopped after 19 minutes, the supermice ran on average for 31.9 minutes.

"This is not something you would do to humans; it would be completely unethical and even if it were possible, you would have to eat an extraordinary amount of food. But we do know there's a link between exercise and reduced risk of cancer and these mice will help us to study why that is," said Prof Hanson.